<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>my css3</title>
    <style>
        .c4 {
            width: 1000px;
            margin: 0 auto;
        }
        .banner {
            height: 100px;
            background: #5bbbc0;
        }
        .c1, .c2, .c3 {
            width: 333px;
            height: 200px;
            /*border: 1px solid black;*/
            float: left;
        }
        ul {
            list-style-type: none;   /*去掉圆点*/
            padding: 0;
            margin: 0;
        }
        li {
            float: left;
            width: 166px;
            background: #BEBEBE;
        }
        #nav1 {
            width: 170px;
        }
        a {
            display: block;    /*将a转为块元素*/
            height: 30px;
            line-height: 30px;
            color: white;
            text-decoration: none;
            text-align: center;
            font-weight: bold;
            border-bottom: 2px solid #900B09;
        }
        a:hover {
            background: #900B09;
        }
    </style>
</head>
<body>
<div class="c4">
    <div class="banner">banner</div>
    <div class="nav">
        <ul>
            <li><a href="#">HOME</a></li>
            <li><a href="#">NEWS</a></li>
            <li><a href="#">LINUX</a></li>
            <li><a href="#">SHELL</a></li>
            <li><a href="#">PYTHON</a></li>
            <li id="nav1"><a href="#">HTML</a></li>
        </ul>
    </div>
    <div>
        <div class="c1">div 1</div>
        <div class="c2">div 2</div>
        <div class="c3">div 3</div>
    </div>
</div>
</body>
</html>